The optical fiber communication technology has become one of main pillars of the modern communication, and it plays a pivotal role in the modern telecommunication network. Optical fiber communication is an emerging technology, and its fast speed of development and wide scope of application in recent years are rare in the history of communications, and it is also an important symbol of the new technological revolution in the world and a major tool for transferring various information in the future information society.
With the continuous promotion of the “tri-networks integration” service demands, basically the optical fiber is used as a trunk line in all backbone networks between provinces and countries, in backbone networks within common cities. A backbone network is an important architecture element for constructing an enterprise network. The backbone network provides paths for information interchange between different local area networks or subnetworks. In common cases, the capacity of the backbone network is greater than the capacity of the network connected to the backbone network. The backbone network is a large-scale transport network, and it is used for connecting small-scale transport networks and transmitting data.
Fiber to The Building (FTTB) and Fiber To The Home (FTTH) have also become the best means for solving the bandwidth bottleneck problem of the access network, and the passive optical network technology is much popular for its advantages such as high bandwidth, long-distance transmission and point-to-multipoint topology and so on, and it has become a main application architecture for various countries deploying the FTTH and FTTB. A Passive Optical Network (PON) is a passive optical access technology using a point-to-multipoint topological structure. At present, an xPON system has been largely deployed to be commercial at home and abroad, and meanwhile, the operation maintenance technology of the PON network is also continuously developed and strengthened.
The Optical Time-Domain Reflectometer (OTDR) technology has a very important significance in the maintenance of optical network fault. Major indexes of the OTDR technology include a dynamic range, a spatial resolution and a dead zone and so on. Wherein, the dynamic range is related to a noise level of a practical circuit, an effective measuring range of an Analog-Digital Converter (ADC) and a resolution of the ADC. In a receiving circuit, reducing an offset voltage of the receiving circuit and a zero drift of the operational amplifier is conducive to improving the effective measuring range of the ADC and improving the detectability of the OTDR. In an OTDR receiving circuit, since the variation of amplitude of optical signals required to be detected is large, in order to ensure that small signals can be detected, a higher link gain is required to be designed, and the influence from the offset voltage of the pre-stage circuit including the dark current of optical devices will be amplified in the post-stage circuit, and the consequence is occupying a larger dynamic range of the ADC, thereby affecting the dynamic range which the system reaches. A manual zeroing method is used in the receiving circuit of the OTDR instrument, before performing measurement, zeroing is manually performed on an operational-amplifier zeroing terminal. A zeroing function can be completed well in this way, but it is not intelligent, which increases the manual complexity of the test. Another common zeroing method is an automatic zeroing method, and intervention by software is not required in such zeroing method, but the direct current component and low frequency component thereof will be affected, and the consequence is that a tested waveform is worse, which influences the identification of the OTDR event point.